On the design of circuits for frequency synthesizers at MM-waves in ultra scaled CMOS

Transceivers for wireless communications at millimeter-waves are becoming pervasive in several commercial fields. Taking advantage of a cut-off frequency of hundreds of GHz, CMOS technology is rapidly expanding from Radio Frequency to Millimeter-Waves, thus enabling low-cost compact solutions. The question we raise in this talk is whether scaling is just providing advantages at mm-waves or not. We present experimental data of single devices, comparing 65nm and 32nm nodes in a wide-frequency range. In particular, switches used in VCOs for tank components tuning, MOM and AMOS capacitors, inductors. fT and fMAX increase though slower than in the past, ron*Coff, a figure of merit for switches, improves correspondingly. As a consequence, wide-band circuits benefit from scaling to 32nm. As an example, a frequency divider-by-4, based on differential pairs used as dynamic latches, realized in both technology nodes and able to operate up to 108GHz, is discussed. On the contrary, passive components do not improve and eventually degrade their performances. As a consequence, a conventional LC VCO, relying on tank quality factor, is not expected to improve. In this work we discuss a new topology for Voltage Controlled Oscillators, based on inductor splitting, showing low noise and wide tuning range in ultra-scaled nodes.